1. Field of the Invention
The present invention relates to a zoom lens barrel of a camera and in particular, relates to an apparatus for preventing a leakage of light therefor.
2. Description of the Related Art
In a zoom lens barrel in which the focal length is varied by moving a plurality of lens groups which are relatively rotatable in the optical axis direction, various barrels (cylindrical members) are provided to perform the zooming operation. These barrels are provided with light interception devices for preventing harmful light from entering a space between the barrels.
For instance, in a lens barrel whose position is restricted by a cam mechanism, light enters a radial space between a cam ring and an inner barrel. To prevent this, it is necessary to provide a light interception member made of a rubber, separate from the barrel, at a front end of the barrel. However, since the rubber light interception member is expensive and is usually pressed onto the outer peripheral surface of the barrel which is reciprocally moved in the optical axis direction, the light interception member applies a certain load to the feed mechanism of the lens barrel, and thus, the service life of batteries may be shortened.
In a lens barrel in which the lens barrel is moved via a helicoid engagement, some of the threads of the helicoids overlap in the optical axis direction, and hence no light reaches the inner barrel portion behind the helicoids. Therefore, a light interception device is not necessary.
It is an object of the present invention to prevent light from leaking in a lens barrel whose position is restricted by a cam mechanism without using a separate or additional light interception means.
To achieve the object mentioned above, according to the present invention, an apparatus for preventing a leakage of light in a zoom lens barrel is provided, including a pair of cylindrical members which at least partly overlap in the radial direction and which are relatively rotatable and relatively movable in an optical axis direction; a drive mechanism which reciprocally moves one of the cylindrical members in the optical axis direction relative to the other cylindrical member of the pair of cylindrical members when the other cylindrical member is rotated; and helical light interception projections that are provided on opposed peripheral surfaces of the pair of cylindrical members so as not to screw-engage with each other. The helical light interception projections are adapted to prevent light from entering a space between the pair of cylindrical members while permitting the pair of cylindrical members to relatively rotate and relatively move in the optical axis direction.
In an embodiment, the pair of cylindrical members include a rotary feed cylinder and a linear movement cylinder which is arranged in the rotary feed cylinder. The drive mechanism includes a linear movement guide cylinder which is arranged in the linear movement cylinder and which is rotatable relative to the rotary feed cylinder but is not movable in the optical axis direction relative to the rotary feed cylinder, the linear movement guide cylinder being guided to linearly move in the optical axis direction; a linear movement guide slot which is formed on the linear movement guide cylinder and which extends in the optical axis direction; a cam groove which is formed between adjacent the helical light interception projections provided on the inner peripheral surface of the rotary feed cylinder; and a guided member which is secured to the linear movement cylinder, wherein the guided member engages with both the linear movement guide slot of the linear movement guide cylinder and the cam groove of the rotary feed cylinder.
Preferably, a moving lens group is further included in the linear movement guide cylinder, the moving lens group being secured to the guided member through the linear movement guide slot, so that the moving lens group is moved together with the linear movement cylinder in accordance with the axial movement of the linear movement cylinder relative to the rotary feed cylinder.
According to another aspect of the present invention, an apparatus for preventing a leakage of light between a pair of cylindrical members is provided, which at least partly overlap in the radial direction and which are relatively rotatable and relatively movable in an optical axis direction, including a drive mechanism which reciprocally moves one of the pair of cylindrical members in the optical axis direction relative to the other cylindrical member of the pair of cylindrical members when the other cylindrical member is rotated; and helical light interception projections that are provided on opposed peripheral surfaces of the pair of cylindrical members so as not screw-engage with each other. The helical light interception projections are adapted to prevent light from entering a space between the pair of cylindrical members while permitting the pair of cylindrical members to relatively rotate and relatively move in the optical axis direction.
Preferably, the pair of cylindrical members include a rotary feed cylinder and a linear movement cylinder which is arranged in the rotary feed cylinder. The drive mechanism includes a linear movement guide cylinder which is arranged in the linear movement cylinder and which is rotatable relative to the rotary feed cylinder but is not movable in the optical axis direction relative to the rotary feed cylinder, the linear movement guide cylinder being guided to linearly move in the optical axis direction; a linear movement guide slot which is formed on the linear movement guide cylinder and which extends in the optical axis direction; a cam groove which is formed between adjacent the helical light interception projections provided on the inner peripheral surface of the rotary feed cylinder; and a guided member which is secured to the linear movement cylinder, wherein the guided member engages with both the linear movement guide slot of the linear movement guide cylinder and the cam groove of the rotary feed cylinder.
Preferably, a moving lens group is further provided in the linear movement guide cylinder, the moving lens group being secured to the guided member through the linear movement guide slot, so that the moving lens group is moved together with the linear movement cylinder in accordance with the axial movement of the linear movement cylinder relative to the rotary feed cylinder.
The present disclosure relates to subject matter contained in Japanese Patent Application No.11-323859 (filed on Nov. 15, 1999) which is expressly incorporated herein by reference in its entirety.